I don't know if this even applies to anyone OTHER than Potsie on Happy Days, so I really am curious what you folks have to think on the topic.
On Happy Days, the driving plot of the series for the first seven seasons is the idea of a teen and his two best friends getting through high school and college with the help of their cool, street smart older friend (while the teen, in turn, lets the cool friend be part of a family that he never had growing up).
In Season 8, that changes when Ron Howard left the show. Don Most left with him. So now the show turns into being about the romance of two teens, one of whom is the sister of the departed lead and the other is the cousin of the cool, street smart guy. So now he works as a mentor to these teens. All said and done, it was a pretty impressive transition that kept the show quite popular (which falls apart after two seasons when those teens leave town for a spin-off).
In any event, as I noted, the driving force of the sitcom leaves after seven seasons, as does one of his friends. However, one friend stays behind. Anson Williams, the actor who plays Potsie, decides to stick around on the show. Since he was a big part of the first seven seasons, the showrunners gladly kept him. Thing is, there was no real place for him anymore. Still, they're paying him, so they find things for him to do, often stretching credulity to its limit (The episode is at the high school basketball game - the announcer of the game is Potsie! Fonzie is up for a teacher's award - the emcee of the event is Potsie!). They eventually tried to address it by making Potsie work for Mr. Cunningham at the hardware store, but even that wouldn't really explain why he'd be involved in the plots on the show.
Because of the difficulty of working him into the show, he would miss chunks of episodes at a time, and actually did not appear in the last few episodes of the series (including the finale).
So what I'm asking is - can you think 0f other examples of this scenario? If so, how did that show deal with it?